America has not had an overweight president since William Howard Taft, who, in the most memorable moment in American history (according to 4th-graders) got stuck in the White House bathtub and had to be rescued by aides. (In Taft's defense, he was also the first president to throw out the first ball at a baseball game, so it wasn't like he did nothing all day all the time.)
Could voters be softening their stance on corpulent commanders-in-chief? The Daily Beast's Lloyd Grove notes four of the most bandied-about names for the GOP nomination in 2012--former Mississippi Gov. Haley Barbour, New Jersey Gov. Chris Christie, former House Speaker Newt Gingrich, and former Arkansas Gov. Mike Huckabee--have physiques that do not conform, in Grove's words, to the "telegenic stereotype of lean and hungry strivers."
But that might not be a bad thing. As Grove notes, while these candidate have less-than-ideal physiques for say, triathletes, or an NFL free safety, they're in peak condition for campaign trail hobnobbing. Barbour in particular "who made a point of cultivating establishment journalists, often over tumblers of Maker’s Mark, when he was a political operative, Washington lobbyist, and successful chairman of the Republican National Committee" is using that chumminess to become "a favorite of the media elite, many of whom could afford to shed a few pounds."
Once again, it all comes down to identity politics.